Bionic Vision Australia - Implantation of a suprachoroidal retinal prosthesis- results for the first participants

Abstract

Purpose: Three participants with severe vision loss due to retinitis pigmentosa were implanted with a silicone / platinum retinal prosthesis into the suprachoroidal space to determine whether electrical stimulation of the device in this location could elicit phosphenes within safe charge density limits. The surgical procedure was developed in human cadavers and modified from that used in animal studies. A percutaneous pedestal was used to enable stimulation of the electrode.

Methods: A retinal prosthesis with twenty-two x 400 or 600 μm diameter electrodes and two return electrodes was implanted into three patients, all with bare light perception vision. The device was inserted into the eye via a scleral wound beneath lateral rectus. The array was placed beneath the fovea in all three patients. The lead exiting the eye was sutured to the sclera and passsed deep to the temporalis fascia to the pedestal situated superior to the pinna. The array impedances were checked intra and post operatively.

Results: In all three patients the array was able to be implanted in the suprachoroidal space with no intraoperative complications. Direct visualization confirmed the position of the array beneath the macula. During the first two postoperative weeks subretinal haemorrhage developed in all three patients. In all cases this cleared spontaneously and has not recurred. Electrical impedance checks confirmed that all electrodes were functional and stimulation has commenced on two patients. Reproducible well defined phosphenes could be elicited within acceptable safe limits. Over three to six months postoperatively electrical thresholds have reduced and both the thresholds and electrical impedances have stabilised.

Conclusions: The surgical procedure to implant a suprachoroidal retinal prosthesis is straightforward and reproducible. Early postoperative intraocular haemorrhage occurred but this cleared spontaneously and has not been detrimental. The position of the device is stable and impedances confirmed that all electrodes within the arrays were functional post implantation. Electrical stimulation of the electrode array results in reproducible phosphenes with stable thresholds. Continued function of the devices over months has confirmed the robustness of the arrays and lead wires.

Keywords: 688 retina • 696 retinal degenerations: hereditary • 762 vitreoretinal surgery